How to skip record if id already exist in target

I'm doing a FT using DM Tool for account balance migration, in that case if that account has already balance, then how should I skip the records.

Please some one help me on this..It's urgent.

what is the type of FT table ID?

FT Transaction Type is 'AC' and if account balance already exist ,we need to skip those account to proceed further.

there are two ways:
1- extract existing data from FT table and compare it with the new data manually.
2- write a validation routine and attach it to the OFS.VERSION to check if the (CREDIT/DEBIT) account have any balance then through an error message.

if you choose to go with option 2 then you have to change the OFS.SOURCE to DM.OFS.SRC.VAL or create your own to validate data before inserting.